834  PRE-CAMBRTAN    GEOLOGY   OF    NORTH    AMERICA. 
every  gradation  from  unchanged  fossiliferous  limestone  to  completely 
metamorphosed  rock,  melted  material  sometimes  being  found  thrust 
into  the  seams  of  the  unchanged  mass.  The  core  of  Laramie  Peak  is 
of  granite,  while  around  it,  as  if  thrown  off  by  this  nucleus,  is  a  series 
of  Azoic  stratified  rocks  consisting  of  gneiss,  hornblendic,  micaceous, 
and  talcose  slates,  syenite,  and  quartz,  which  are  cut  here  and  there  by 
dikes  of  trap  or  basalt. 
Hayden,61  in  1868,  mentions  granites  and  syenites  as  occurring  in 
the  Laramie  and  Medicine  Bow  ranges.  On  the  east  side  of  Laramie 
Range,  especially  near  Fort  Laramie,  are  seen  the  distinctly  dis- 
cordant relations  between  the  crystalline  rocks  of  the  mountain  range 
and  the  unmetamorphosed  strata. 
Hayden,34  in  1872,  describes,  on  one  of  the  branches  of  the  Chug- 
water,  in  the  Laramie  Mountains,  as  occurring  interstratified  with 
red  feldspathic  granite,  beds  of  magnetic  ore  which  resemble  the 
Lake  Superior  iron  ores.  The  rocks  between  the  headwaters  of  the 
Chugwater  and  Laramie  consist  of  beds  of  quartz,  black  gneiss,  seams 
of  feldspar,  with  now  and  then  beds  of  massive  granite.  On  ap- 
proaching the  mountains  the  red  feldspathic  granite  is  found  in  great 
ridges,  the  gneissic  strata  diminishing  and  the  massive  granite  in- 
creasing in  approaching  the  mountain  range. 
Engelmann,108  in  1876,  finds  that  the  Laramie  Peak  system  con- 
sists of  the  igneous  rocks  granite  and  granitic  syenite.  Among  the 
igneous  rocks  are  also  greenstones,  which  are  of  later  date  than  the 
granite,  in  which  they  frequently  are  dikes. 
Hague,35  in  1877,  gives  detailed  descriptions  of  the  Laramie,  Medi- 
cine Bow,  and  Park  ranges.  The  Archean  rocks  of  the  Laramie  Hills 
are  classed  under  granites,  gneiss,  mica  schist,  and  hornblende  schist, 
the  first  covering  much  the  largest  area.  The  central  body  consists 
of  coarse-grained  granite.  Above  this,  and  forming  the  outer  edges, 
dipping  east-west,  away  from  the  main  mass,  occur  heavily  bedded 
granitoid  rocks.  At  the  north  and  south  ends  of  the  range  the  gran- 
ites gradually  pass  into  well-defined  gneisses  and  schists,  there  being 
the  most  gradual  transitions  from  the  massive  granites  to  the  thinly 
laminated  schists.  Among  the  crystalline  rocks  is  a  variety  of  gab- 
bro  in  the  region  of  Iron  Mountain  and  Chugwater  and  Horse  creeks, 
where  it  forms  knobs  and  knolls  protruding  through  the  granitoid 
rocks.  At  Iron  Mountain,  north  of  Chugwater  Creek,  are  masses  of 
titaniferous  iron  ores  incased  in  the  granite.  No  large  bodies  of 
eruptive  granites  were  seen,  nor  eruptive  rocks  younger  than  the 
Archean.  In  structure  the  Laramie  Hills  are  regarded  as  a  broad 
anticline,  accompanied  by  many  secondary  folds.  There  is  no  case 
of  decided  unconformity  in  the  entire  series  of  beds,  and  their  uni- 
form character  indicates  that  they  all  belong  to  one  division  of  the 
Archean,  which,  without  doubt,  is  the  Laurentian.    The  sedimentary 
